Constructing large 3D meshes

[lukem12345]

PR #60 added support for 3D dual complexes, building off PR #57 which added support for 3D simplicial sets.

Currently, we can thoroughly test 2D operators on meshes constructed programmatically or read in from .obj files.

In 3D, we can construct meshes by gluing single tetrahedra, or using the glue_sorted_tet_cube! function, which adds tesselated cubes to a mesh.

• We should find a way to load in 3D tesselated spaces from whichever file formats are convenient. Hopefully we can keep using GeometryBasics.Mesh objects
• We should add a helper function for creating meshes of many more tetrahedra, analagous to the triangulated_grid function.

This will enable larger scale tests of our differential operators in 3D.